5 line Apollo Server GraphQL Type resolver efficiency proof of concept

mapAttributes.js

const mapAttributes = (model, { fieldNodes }) => {
  // get the fields of the Model (columns of the table)
  const columns = new Set(Object.keys(model.rawAttributes));
  const requested_attributes = fieldNodes[0].selectionSet.selections
    .map(({ name: { value } }) => value);
  // filter the attributes against the columns
  return requested_attributes.filter(attribute => columns.has(attribute));
};

poc.js

...
User: async (
    _, // instance (not used in Type resolver)
    { username, ... }, // arguments 
    { models: { User }, ... }, // context
    info,
  ) => {
    if (username) {
// before (entire row queried)
    // return User.findOne({ where: { username } }); ...
        
// after (only requested columns queried)
      return User.findOne({
        where: { username },
        attributes: mapAttributes(User, info),
      });
    } ... 
  }
...

Hey there, I ran into some issues when running this with a nested selection set i.e.

query {
  user {
    posts {
      id
      comments {
        title
        author {
          id
        }
      }
    }
  }
}

To help resolve this, I came up with the following edits:

const mapAttributes = (model, { fieldNodes }) => {
  // get the fields of the Model (columns of the table)
  const columns = new Set(Object.keys(model.rawAttributes));
  // get nested attributes for each selection set
  const nested_attributes = selectionSet =>
    (selectionSet &&
      selectionSet.selections &&
      selectionSet.selections.reduce(
        (acc, { name: { value }, selectionSet }) =>
          new Set([...acc, value, ...nested_attributes(selectionSet)]),
        new Set()
      )) ||
    [];
  const requested_attributes = nested_attributes(fieldNodes[0].selectionSet);
  // filter the attributes against the columns
  return [...requested_attributes].filter(attribute => columns.has(attribute));
};

Hope this helps!

nice man. thanks for the update. do you have a medium account? i can update the article and credit you